Inductance (measured in henries H) is an effect which results from the magnetic field that forms around a current-carrying conductor. The electrical current through the conductor creates a magnetic flux proportional to the current. A change in this current creates a change in the magnetic flux that, in turn, generates an electromotive force (EMF) that acts to oppose this change in current. Inductance is a measure of the generated EMF for a unit change in current. The number of turns, the area of each loop/turn, and what it is wrapped around affect the inductance. For example, the magnetic flux linking these turns can be increased by coiling the conductor around a material with a high permeability.
The energy stored by an inductor is equal to the amount of work required to establish the current flowing through the inductor, and therefore the magnetic field. This is given by:
      E    stored    =            1      2        ⁢          LI      2      
where:                L is the inductance; and        I is the current flowing through the inductor.        
An inductor is commonly constructed as a coil of conducting material, such as copper wire, wrapped around a core either of air or of a magnetic material. Core materials with a higher permeability than air confine the magnetic field closely to the inductor, thereby increasing the inductance. Inductors come in many shapes. For example, many common inductors are constructed as enamel coated wire wrapped around a ferrite bobbin with wire exposed on the outside, while some enclose the wire completely in ferrite and are called “shielded”. Some inductors have an adjustable core, which enables changing of the inductance. Inductors that can be used to block very high frequencies are sometimes made with a wire passing through a ferrite cylinder or bead. Small inductors can be etched directly onto a printed circuit board by laying out a trace in a spiral pattern. Small value inductors also can be built on integrated circuits using the same or similar processes that are used to make transistors. In these cases, aluminum interconnect is commonly used as the conducting material.
The Q factor of an inductor can be found through the following formula, where R is its internal electrical resistance:
  Q  =            ω      ⁢                          ⁢      L        R  
By using a magnetic core, the inductance is increased for the same amount of copper, raising the Q. The cores, however, also introduce losses that increase with the frequency. A grade of core material is chosen for best results for the frequency band.
A basic inductance formula for a cylindrical coil is:
  L  =                    μ        0            ⁢              μ        r            ⁢              N        2            ⁢      A        l  
where:                L=Inductance in henries (H);        μ0=permeability of free space=4π×10−7 H/m;        μr=relative permeability of core material;        N=number of turns;        A=area of cross-section of the coil in square meters (m2); and        l=length of coil in meters (m).        
Inductors are used extensively in analog circuits and signal processing. Inductors in conjunction with capacitors and other components can be used to form tuned circuits that can emphasize or filter out specific signal frequencies. Smaller inductor/capacitor combinations can provide tuned circuits that can be used in radio reception and broadcasting. For analog/RF and system on chip (SOC) applications, inductors can be required to be a basic element.
FIGS. 1 and 2 show a conventional serpent type inductor having an inductor metal 110 coupled to bottom metal 112 by a via interconnect 114. As shown in the cross-sectional illustration in FIG. 2, a cap film 120 is formed on an inter layer dielectric (ILD) 122. The inductor metal 110 is formed on the cap film 120. The conventional inductor commonly uses an oxide or a low-k oxide as an isolation film 108 and/or a high-k cap film 120.